Weeping Cherry Issues

Hello, I am not very knowledgeable about tree. My nursery planted a weeping cherry in my front yard in October of last year. I live in Vacaville, CA where it is quite hot and it gets full sun. In June the leaves started getting holes in them and then the ends turned brown. Now I have some yellow leaves, some brown at the tip, and some died and fell off. One branch is completely bare. I was watering once a week, a long slow 2 hour soak from the hose near the trunk. I recently went to every 10 days on advise from the nursery. I know the soil has a lot of clay. There are about four small areas on the limbs where a little sap has oozed out. I have never fertilized the tree. Does anyone have any ideas about what is causing my tree's problems?